A heating unit of this type is known from U.S. Pat. Nos. 3,612,828 and 3,624,352, in which a large block of insulating material lies in a support tray and an insulating support which is also large with a raised edge and a raised central zone lies on this block of insulating material. An annular region is milled out to form a relatively flat radiation chamber. Heating resistances in the form of meanderingly curved heating strips are inserted in grooves on its base. This heating unit has the disadvantage of having a substantial height and can therefore be used only in cooking stoves and not in flat fitted troughs. The thickness of the insulating material results particularly from the fact that the insulating support must consist of a material with high mechanical strength which consequently has a lower insulating capacity and is a greater conductor of heat. In addition, this insulating support is heated relatively greatly by the heating resistances and the upward radiation face is small. An electric cooker appliance with a glass ceramic plate is known from German Offenlegungschrift No. 21 65 569, the heating unit of which has radially running insulating webs on a sheet metal support, which insulating webs guide the heating coil relatively closely beneath the glass ceramic plate. The sheet metal support is located in a support tray and is lined with insulating material. This design requires the use of numerous insulating webs on the support plate composed of metal. The distance from the glass ceramic plate is small and special steps have to be taken to satisfy the requirements of resistance to impact and protection from contact in the case of possible breakage of the glass ceramic plate. The heating unit has to be completed before insertion of the heating coils and can only be exchanged in its entirety. Moreover, it is laborious to insert the spirals into the insulating webs. The heating coils tend to sag and may need intermediate supports, particularly if the thickness of the wire has to be small owing to the use of a high operating voltage.